21161780 has 24 divisors (see below), whose sum is σ = 45642408. Its totient is φ = 8235648.

The previous prime is 21161779. The next prime is 21161783. The reversal of 21161780 is 8716112.

It can be written as a sum of positive squares in 4 ways, for example, as 13118884 + 8042896 = 3622^2 + 2836^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21161783) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13559 + ... + 15038.

It is an arithmetic number, because the mean of its divisors is an integer number (1901767).

Almost surely, 2^21161780 is an apocalyptic number.

21161780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21161780 is an abundant number, since it is smaller than the sum of its proper divisors (24480628).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21161780 is a wasteful number, since it uses less digits than its factorization.

21161780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28643 (or 28641 counting only the distinct ones).

The product of its (nonzero) digits is 672, while the sum is 26.

The square root of 21161780 is about 4600.1934741921. The cubic root of 21161780 is about 276.5990802796.

Adding to 21161780 its reverse (8716112), we get a palindrome (29877892).

The spelling of 21161780 in words is "twenty-one million, one hundred sixty-one thousand, seven hundred eighty".